which carb to upgrade/replace too

[Lou C]

Also there are other things that can cause fuel delivery problems, such as a fuel pick up tube with a clogged filter, or a blocked/corroded anti siphon valve.
I rigged this up to test mine for leaks, both were fine, my performance problems were simply from bad gas this past season. I tested it to -10" of mercury which is what a mechanical fuel pump pulls usually. I found that a good anti siphon valve opens between -1-->2" of mercury
The way to rule these causes out is simply hook up an outboard fuel tank to the fuel pump and run the boat on that. If you still have problems, it's definitely the carb, but if it runs perfect it's the boat fuel system. So, you'll be pulling the fuel pick up tube and looking at the anti siphon valve.
When I did that, the boat leaped up on plane and ran perfect. Shoulda done that before going through the points and cleaning/rebuilding the Quadrajet!
PS if you do this it's a good idea to put a shut off valve on it, in case the fuel line to the pump leaks! Use good clamps too!

 

[bigtoe]

to the OP: As a second opinion,
Danforth is right.

Many thanks

 

[bigtoe]

Also there are other things that can cause fuel delivery problems, such as a fuel pick up tube with a clogged filter, or a blocked/corroded anti siphon valve.
I rigged this up to test mine for leaks, both were fine, my performance problems were simply from bad gas this past season. I tested it to -10" of mercury which is what a mechanical fuel pump pulls usually. I found that a good anti siphon valve opens between -1-->2" of mercury
The way to rule these causes out is simply hook up an outboard fuel tank to the fuel pump and run the boat on that. If you still have problems, it's definitely the carb, but if it runs perfect it's the boat fuel system. So, you'll be pulling the fuel pick up tube and looking at the anti siphon valve.
When I did that, the boat leaped up on plane and ran perfect. Shoulda done that before going through the points and cleaning/rebuilding the Quadrajet!
PS if you do this it's a good idea to put a shut off valve on it, in case the fuel line to the pump leaks! Use good clamps too!

View attachment 414535
View attachment 414534

Thanks for the info, now the old fuel last year they said was bad, so they did as you did and fitted the outboard tank to run it up in there work shop. Told me to empty and clean the tank , which I did . I didn’t think the fuel looked to bad , and not really any dirt in there as I cleaned it out two years ago.
So my question is , where would the anti siphon valve be? I’ve not heard of that before , this could also be part of the problem!
Thanks

 

[Scott Danforth]

its the barbed fitting on the tank

 

[Lou C]

Yep in my pic above you see the alu pick up tube, the anti siphon is screwed into that on the left side of the pic, with the rubber fuel hose attached to it. They can be tough to remove, if not removed for a long time. On mine I got lucky, both the anti siphon and the pick up tube came out easily. The fuel tank and pick up tube are 38 years old! The anti siphon valve was replaced back in 2004. Still good though. This tube didn't have a screen on it but some do and cause fuel starvation, you won't know unless you pull out that tube.
When I first bought this boat in 2002 the engine would start and run at idle fine and would move the boat at idle and just above but would not plane off the boat. So the mechanic I used at the time found the anti siphon valve was stuck and the carb needed to be rebuilt and it was fine after that.

 

[Lpgc]

Had a problem with a stuck anti-syphon valve on my boat's tank too, was advised to remove and clean it by some of the same people who have posted on this thread, fixed it. Before fixing it would run OK up to about half throttle but lean off or cut out if I gave it more throttle. IIrc there was a ball bearing in it which had become stuck in the near closed position, cleaning it all up inside and getting that ball freed off was a complete fix.

 

[bigtoe]

Well I will say mine has had similar issues , at times, possibly it jams then frees itself .
I normally find I have two issues going on, I do know that fitting , I tried to remove it last year to aid cleaning the tank. Tight as a tiger it is. I’ll have to try harder . Thanks

 

[Lou C]

I made the sign of the cross and said a couple Hail Marys before trying to get mine loose! And sprinkle Kroil and Freeze off etc like holy water! Time, patience will get it done.